in my house i have two rings or two tabtops between the support bracket and the fennial (just to hold the curtain in place) and then by eye we just pulled the fennial out a bit so you can see it as a feature, same distance out on both sides.
saying that we'v all metal ones that run the lenght of two metre long windows so had no cutting etc.
Id go by your eye as after there up you'll never really look at them again.....